Because of recent advances in precision engineering that allow controlled grinding infeed rates as small as several nanometers per grinding wheel revolution, it is possible to grind brittle materials so that the predominant material-removal mechanism is plastic-flow and not fracture. This process is known as ductile-regime grinding. When brittle materials are ground through a process of plastic deformation, surface finishes similar to those achieved in polishing or lapping are produced. Unlike polishing or lapping, however, grinding is a deterministic process, permitting finely controlled contour accuracy and complex shapes. In this paper, the development of a research apparatus capable of ductile-regime grinding is described. Furthermore, an analytical and experimental investigation of the infeed rates necessary for ductile-regime grinding of brittle materials is presented. Finally, a model is proposed, relating the grinding infeed rate necessary for ductile material-removal with the properties of the brittle workpiece material.

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The accuracy of precision machining operations could be improved through tool force feedback. Tool force is ideally suited for use in a control algorithm because it contains information on the instantaneous depth of cut, feed rate and condition of the tool. A tool force model that could form the basis of this new control technique has been developed. By measuring the shear angle from micrographs of chip cross sections, equations for the forces due to chip formation and the friction between the chip and the tool have been written. Furthermore, the effects of elastic deformation of the workpiece (spring back) on chip formation and the measured forces, which can be significant in precision machining, have been included in the model. Machining experiments were conducted with a 0 deg rake diamond tool and four metals that are commonly diamond turned. For machining with newly lapped as well as worn tools, the calculated forces were in excellent agreement with the measured values for the array of workpiece materials.

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Chemically assisted ion beam etching (CAIBE) characteristics of gallium nitride (GaN) have been investigated using a 500-eV Ar ion beam directed onto a sample in a Cl2 ambient. Enhanced etch rates were obtained for samples etched in the presence of Cl2 over those etched only by Ar ion milling at a substrate temperature of 20 °C. The CAIBE etch rates were further enhanced at higher substrate temperatures whereas etch rates for Ar ion milling were not influenced by substrate temperature. Etch rates as high as 210 nm/min are reported. The etch rates reported here are the highest so far reported for GaN. Anisotropic etch profiles and smooth etched surfaces in GaN have been achieved with CAIBE.